As is well known, the conventional and widely used prong-type stacked paper fastener works well when used to bind thin files. However, as the file gets thicker over a period of time it tends to work loose and starts to "rotate" in the file covers. Eventually it works so loose that the file proprietor must either tighten the fastener, or reduce the thickness of the file. Otherwise, the more the file is handled the looser the component papers become.
It is the general purpose of the present invention to provide a prong type fastener which overcomes the foregoing problem and which maintains even thick files in permanently stable condition.
It is a further object of the invention to provide a prong-type fastener in which the foregoing important advantage is achieved by a simple modification of the currently popular "ACCO" type fastener, which modification does not require expensive changes in manufacturing and/or use techniques.
Another object of the present invention is the provision of a prong-type fastener for stacked sheet materials which is inexpensive, safe to apply, quick and easy to use, and of long service life.
Still a further object of the present invention is the provision of a prong-type stacked paper fastener which may be manufactured from a variety of thin sheet materials such as plastic or sheet metal by a simple stamping procedure.
The foregoing and other objects are achieved by the provision of a prong-type fastener for stacked sheet materials which comprises a sheet retainer component and a compressor component. These components are of the general character of the corresponding components of the prong-type fasteners of the prior art. However, the prongs of the sheet retainer component are formed with a plurality of longitudinally spaced perforations and the openings of the compressor component which receive the prongs are provided with tang means dimensioned and arranged for releasable insertion in selected ones of the prong perforations.
Additionally, the compressor component is provided with a slide lock having a locking detent which enters a selected perforation of the bent over portion of the associated prong. This prevents inadvertent displacement of the slide lock during use of the file. In this manner the compressor is secured snugly against the sheet stack upon bending of the prongs to their operative positions.
As a further feature, the fastener may be applied in novel manner by interengaging the first prong and tang means at one end of the fastener assembly in a first step and using the compressor as a lever for further compressing the stacked sheets preliminary to interengaging the second prong and tang means at the other end of the fastener assembly in a second step, thereby insuring the production of a tightly fastened stack.